Detect suspicious AD SelfService web requests targeting report generation and API endpoints

Flags web requests with URL query strings targeting known ADSelfService exploitation paths for CVE-2021-40539.

FreeReviewedSigma · High · v5

Category: webserver
Author: Tobias Michalski (Nextron Systems), Max Altgelt (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2021-09-20
Updated: 2026-07-31

ATT&CK techniques

Initial Access

Recon
Resource Dev
Initial Access
- T1190Exploit Public-Facing Application
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags webserver activity where the requested URL query contains specific path fragments associated with AD SelfService exploitation attempts. Attackers may use these crafted requests to reach vulnerable report generation and servlet/rest API functionality. The detection relies on webserver telemetry capturing the full request URI query string (cs-uri-query) and matches the presence of the listed endpoint patterns.

Reporting behind it

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Detect suspicious AD SelfService web requests targeting report generation and API endpoints

Pivot detection · T1190 · 9 related

Changelog

v5
Candidate ingested via manual entry.2026-07-31
v4
Candidate ingested via manual entry.2026-07-31
v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

adselfservice-exploitation-attempts-via-suspicious-web-url-paths-cve-2021-40539-6702b13c

title: Detect suspicious AD SelfService web requests targeting report generation and API endpoints
id: 0ef66e2c-ef4c-4496-b129-9485cdcb101a
status: test
description: This rule flags webserver activity where the requested URL query contains specific path fragments associated with AD SelfService exploitation attempts. Attackers may use these crafted requests to reach vulnerable report generation and servlet/rest API functionality. The detection relies on webserver telemetry capturing the full request URI query string (cs-uri-query) and matches the presence of the listed endpoint patterns.
references:
  - https://us-cert.cisa.gov/ncas/alerts/aa21-259a
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-40539/web_cve_2021_40539_adselfservice.yml
author: Tobias Michalski (Nextron Systems), Max Altgelt (Nextron Systems), Huntrule Team
date: 2021-09-20
modified: 2023-01-02
tags:
  - cve.2021-40539
  - detection.emerging-threats
  - attack.initial-access
  - attack.t1190
logsource:
  category: webserver
detection:
  selection:
    cs-uri-query|contains:
      - /help/admin-guide/Reports/ReportGenerate.jsp
      - /ServletApi/../RestApi/LogonCustomization
      - /ServletApi/../RestAPI/Connection
  condition: selection
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 6702b13c-e421-44cc-ab33-42cc25570f11
    type: derived

Convert

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